1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for improved signaling over satellite-terrestrial networks and, in particular, to providing Internet Protocol signaling over the terrestrial network portion of a satellite-terrestrial telecommunications system.
2. Background and Objects of the Present Invention
The evolution of wireless communication over the past century, since Guglielmo Marconi""s 1897 demonstration of radio""s ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi""s discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well as this wireless network interacts with and eventually overtakes the existing wireline networks.
With reference now to FIG. 1 of the drawings, there is illustrated a Global System for Mobile Communications (GSM) Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Services Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 12 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g. a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless. The MS also includes a Subscriber Identity Module (SIM) 13, which provides storage of subscriber related information, such as the International Mobile Subscriber Identification (IMSI) 15, which uniquely identifies a subscriber.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several base transceiver stations 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or Cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g. user profiles, current location information, IMSI number, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the MSs 20 currently located within the MSC/VLR area 12. If a MS 20 roams into a new MSC/VLR area 123, the VLR 16 connected to that MSC 14 will request data about that MS 20 from the HLR database 26 while simultaneously informing the HLR 26 about the current location of the MS 20. Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to re-interrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
It should be understood that the aforementioned system 10, illustrated in FIG. 1, is a terrestrially-based system. More recently, satellite-terrestrial systems have been deployed which supplement terrestrial systems to provide cellular telecommunications to a wider network of subscribers. One such satellite system, which will be implemented in the near future, is the ICO Global Communications network. Satellite systems have a distinct advantage over more traditional cellular networks in the ability to provide seamless interconnectivity between two geographically remote networks where landline interconnectivity is prohibitively expensive or physically impractical. Furthermore, the satellite network may provide complementary service to the PLMN subscriber by allowing the subscriber to receive cellular service even when the subscriber has roamed outside the geographic area covered by the subscriber""s servicing PLMN.
Shown in FIG. 2 is a representative satellite-terrestrial telecommunications network, generally designated by the reference numeral 205, and hereinafter referred to as a xe2x80x98satellite-terrestrial networkxe2x80x99, which includes a terrestrially-based network and a group or constellation of mid-range satellites 200 that, in a preferred embodiment, provide radio coverage throughout the world. In the satellite-terrestrial network 205, as shown in FIG. 2 of the Drawings, a system of such satellites 200 in orbits above the Earth""s surface are used to provide communication between a number of Mobile Stations (MS) 210 and the satellite-terrestrial network 205.
In an effort to provide seamless interconnectivity between the satellite-terrestrial network 205 and the terrestrial fixed and mobile network 10, the satellite-terrestrial network 205 is equipped with Satellite Access Nodes (SANs) 215 which provide the primary interface between the satellites 200 with other terrestrial networks, e.g. public switched telephone network (PSTN) or public land mobile networks (PLMNs). As shown in FIG. 2, the SAN 215 itself includes a Radio Frequency Terminal (RFT) subsystem 230, which provides the radio interface between the satellites 200 and the SAN 215. Also included in the SAN 215 is a Satellite Base station Subsystem (SBS) 240, which is analogous in function to a combination of the BTS 24 and BSC 23 for GSM-based systems, as described hereinabove with reference to FIG. 1. The SBS 240 coordinates communications to and from the satellites 200 and the respective local systems servicing the area, e.g., other cellular systems coupled to the satellite-terrestrial network 205 and in communication therewith.
Within the satellite-terrestrial network 205, functionality exists in the SBS 240 for evaluating a Service Area servicing the MS 210, generally designated by the reference numeral 250 from which a given system access is being requested. Service Area 250 can, in turn, be mapped onto a specific country or state for the purpose of disabling ciphering or routing emergency calls, e.g., 911 calls to the nearest emergency center in order to meet regulatory requirements and for provisioning appropriate language sets.
With reference again to FIG. 2, a Terrestrial Network Manager (TNM) 280 within SAN 215 performs some of the functions of the BSC 23 of FIG. 1, as well as additional functions unique to satellite based systems, e.g. multi-SAN paging and routing of registration messages to a pertinent MSC/VLR, generally designated by the reference numeral 290. In addition, the TNM 280 consults a database 260, which includes a set of tables, to decide which Channel Managers, contained within the particular SBS 240, to utilize, and which satellite beams should be used for the paging. Thus, SAN 215 provides the primary interface between a network of satellites 200 and any MS 210 in communication therewith and any external networks 270 that MS 210 may in communications with.
Although the benefits of a satellite-terrestrial network 205 are numerous, implementing such a system obviously increases the complexity of the infrastructure and presents a number of disadvantages. For example, in a preferred embodiment, each satellite 200 in the exemplary ICO satellite network provides up to 163 service links supporting up to a total of 4,500 telephone channels of time division multiple access (TDMA) coded speech. To support such a large number of communications, a great deal of inter-node signaling is required in addition to the usual PLMN control and data signaling, as is understood in the art. Particularly, the SANs must be able to quickly relay information regarding a given subscriber between other SANs generally located over great distances.
Additionally, a number of problems exist with conventional satellite-terrestrial networks relating to signaling exchanges between the satellite access nodes. A particularly troubling issue is the reliance of a given SAN 215 on a single MSC 290, which causes routing failures or latency to a subscriber in the event of MSC failure or overload. Additionally, direct inter-SAN communications are generally performed over expensive, leased trunks in a circuit switched manner, the inefficiencies of which are well known and discussed further hereinbelow.
Thus, it is an object of the present invention to provide improved global satellite network access to an Internet Protocol (IP) transport network tailored for a satellite-terrestrial transmission system.
It is another object of the present invention to provide for MSC redundancy and load sharing with respect to servicing a Satellite Base Station Subsystem in a satellite-terrestrial transmission system.
It is a further object of the present invention to provide direct packet routing for speech calls and data calls originating and terminating as circuit-switched data calls in a satellite-terrestrial transmission system.
It is still another object of the present invention to provide improved transmission efficiency without reducing speech quality in a satellite-terrestrial transmission system.
It is yet another object of the present invention to allow transmission over an IP backbone for long-distance and international transit calls in a satellite-terrestrial transmission system.
The present invention is directed to a system and method for a terrestrial IP network for efficient transmissions within a satellite-terrestrial network. The terrestrial network of a satellite-terrestrial telecommunications system provides for IP signaling between satellite access nodes without the use of dedicated, circuit-switched trunks therebetween. The terrestrial network configuration provides for mobile services switching center redundancy and load sharing and well as direct packet routing between satellite access nodes.